1. Field of the Invention
This invention relates to the preparation of methylated aromatic and hydroaromatic compounds, particularly to the preparation of methylated polynucleated aromatics or hydroaromatics. This invention also relates to a process for upgrading highly aromatic feedstocks such as coal-derived, distillate hydrocarbons and certain highly aromatic petroleum-derived hydrocarbons such as FCC clarified slurry oil, TCC syntower bottoms and heavy coker gas oil.
2. Description of the Prior Art
U.S. Pat. No. 2,409,080 discloses the reaction of alkyl mercaptans or sulfides with carbocyclic compounds in the presence of a copper pyrophosphate catalyst to form alkylated cyclic hydrocarbons. Hydrogen sulfide is formed by side reactions in the U.S. Pat. No. 2,409,080 process. The patent teaches that such formed hydrogen sulfide should be removed from unreacted charge stock recovered from the reaction zone.
U.S. Pat. No. 3,718,704 teaches methylation of aromatic hydrocarbons with a carbon-oxide containing reactant gas in the presence of an oxide of a Group IB, IIB and/or VIB metal containing catalysts. The process is preferably carried out in the presence of added hydrogen.
U.S. Pat. No. 4,086,289 discloses a modification of the U.S. Pat. No. 3,718,704 process, supra., wherein the process of methylating toluene to obtain a mixture of xylenes relatively low in the meta-isomer and low in ethyl benzene content by contacting toluene with hydrogen and a carbon oxide-containing gas in the presence of a catalyst, utilizes as the catalyst zinc chromite mixed with an alkali metal exchanged molecular sieve containing a stoichiometric excess of an alkali metal carbonate.
Coal-derived liquids obtained by most direct liquefaction processes are primarily bare ring polynuclear aromatic and hydroaromatic, (i.e. partially saturated) molecules containing few alkyl side-chains. The highly condensed nature of these materials, caused by the hydrodealkylation of the high temperature liquefaction step, makes coal liquids low in cetane number and, therefore, poor components for diesel fuel. Nearly complete hydrogenation of the aromatic rings is needed to obtain high cetane quality material, but thermodynamic limitations to aromatic saturation require very high hydrogen partial pressures (greater than 3000 psi) to obtain high saturation (i.e., less than 10 weight percent aromatics) at reasonable reaction temperatures and contact times. Some petroleum-derived hydrocarbons are also primarily bare ring poly-nuclear aromatics. Examples of such hydrocarbon streams are FCC clarified slurry oil, TCC syntower bottoms, and heavy coker gas oil.
An object of the present invention is to provide an efficient method for upgrading polynuclear aromatic and hydroaromatic feed stocks. A more specific object is to produce a higher cetane quality diesel fuel at a given level of aromatic saturation by raising the hydrogen content of the fuel without direct use of molecular hydrogen. A related object is to provide a method for improving distillate fuel quality by direct methylation. A still further related object of this invention is to provide a method for improving distillate fuel quality without hydrocracking. Another object of this invention is to usefully recover hydrogen from hydrogen sulfide.